I'd say, I would want to be treated by a doctor who is a professional and loves his job. Credentials obviously cannot guarantee both.

sir, you would feel comfortable being treated by a professional road-kill picker-upper who loves his job?

Credentials cannot guarantee that the doctor will love his job and that he has certain degree of professionalism, but it does guarantee that he is at least smart enough to fake through 10 years of med school. Your statement implies that a professional isn't the same thing as credentials, but in the real world where we can't read minds of stranger, most of the time they are the same thing.

That is a very good point. That's why there's got to be something that's going to tell us better than credentials about the person.

Why not? If he has a good, or even exceptional, track-record, are you going to refuse to visit his office because he lacks a degree?

Definitely. A doctor without credentials is not a doctor, he's a witch doctor.

the degree will allow me to find out what sort of training he had prior to practise, what sort of ethical standards he was traditioned under, and guess at his ability to treat something he hasn't seen before based only on "track-record."

For example, if he got his exceptional by cutting people up unnecessarily, and he learns by mistakes instead of learning from a community of certified professionals, it doesn't matter if he's really really good now does it?